A technique is known which is for a vehicle performing idling stop to contribute to reduction of fuel consumption and environmental protection. In this technique, even if idling stop conditions are satisfied, if idling stop prohibition conditions are further satisfied, the idling stop is not performed. However, users cannot determine whether the idling stop has not been performed normally based on prohibition factors or not been performed due to a failure of the vehicle, whereby automobile retailers tend to receive frequent inquiries.
According to the vehicle diagnosis system disclosed in patent literature 1 based on such a background, communication is carried out between a plurality of electronic control units in a vehicle and an external diagnosis unit to perform failure diagnosis for the vehicle. The external diagnosis unit registers a plurality of idling stop conditions for performing idling stop registered in any one of the electronic control units. When the vehicle is stopped in a state where the vehicle is connected with the external diagnosis unit and is being driven, the idling stop conditions that are not satisfied when the idling stop is not performed are displayed on a predetermined display.